apt-get install kde-i18n-ru
Note the "ru" suffix for the desired language, in this case, Russian. Next:
apt-get install kkbswitch
Then, edit /etc/X11/xorg.conf to add the desired alternate keyboard map (in this case, Russian):
as an option under Section "InputDevice".
Optionally, edit the same section of /etc/X11/xorg.conf to add a keyboard switch in addition to the mouseover switch at the panel applet:
Thanks to the community at channel #kde on freenode IRC, and the community at kde-forum.org for the solution.